The coatings industry is constantly searching for new technologies that to will reduce or eliminate the amount of volatile organic compounds (VOCs) in industrial paints and coatings. High solids solvent borne coatings, water based coatings, powder coatings and radiation cured (ultraviolet and electron beam) coatings are technologies that significantly reduce the amount of VOCs relative to traditional solvent borne coatings. Each of the aforementioned technologies has limitations. Thermally cured solvent borne coatings still dominate the industry because suitable substitutes for many coatings have not been found.
With the exception of ultraviolet and electron beam cured coatings and coatings comprising polyallyl glycidyl ethers, (meth)acrylate functional resins and coatings are not used in industrial coating applications. A primary reason for this is that atmospheric oxygen inhibits the curing process. Oxygen inhibited coatings cure at a low rate, often remain tacky, and exhibit poor tensile strength and durability, resulting in film properties that are unsuitable for industrial paints and coatings.
Ultraviolet curing of acrylate films in air is practical because the high density of initiating radicals generated during irradiation consumes dissolved oxygen faster than oxygen can diffuse back into the film. During irradiation, polymerization proceeds in a quasi-anaerobic environment.
Attempts to derive the benefits of free radical chemistry by thermally curing thin, high solids acrylate coatings similar to those used in ultraviolet and 30 electron beam cured coatings have produced under-cured films with marginal solvent resistance. This is true even under practical anaerobic conditions. In practice, the total exclusion of oxygen is difficult in commercial coating operations.
Polyallyl glycidyl ether resins have been used in two-component, high-solids, thermally cured coatings that comprise (meth)acrylate monomers and oligomers. These coatings are two component systems with limited pot life and are expensive due to the high cost of the polyallyl glycidyl ether component. Additionally, they require oxygen and drier compounds such as cobalt carboxylates, and require solvent for spray application. Polyallyl glycidyl ether resins have been commercially available since the early 1990's, but have only achieved very limited use in industrial paints and coatings due to their limitations.
The present invention provides a replacement for many traditional thermally cured solvent borne coatings. In one embodiment of this invention, a solventless coating is provided that can be applied via traditional/existing spray application equipment, and cured in traditional existing cure ovens at traditional cure temperatures and bake times. This embodiment can be characterized as a one-component, storage-stable, solventless, thermally curable, (meth)acrylate functional, clear or highly pigmented paint or coating with a VOC content lower than solvent or water borne coatings and equal to or less than powder coatings. These (meth)acrylate functional coatings can be cured in the presence of atmospheric oxygen. This embodiment is cost competitive with traditional general industrial coatings and is expected to result in a significant reduction in VOC emmisions introduced into the atmosphere.